The present invention relates to magnetic hard disk drives. More specifically, the present invention relates to a system and method for securement of a hard drive magnetic head to a head-gimbal assembly (HGA) to prevent electrostatic discharge (ESD) by the magnetic head.
FIG. 1 provides an illustration of a typical drive arm configuration as used in the art. A magnetic head 108 is utilized to read from and write to a magnetic hard disk. 106. Voice-coil motors (VCM) 102 are used for controlling a hard drive's arm 104 motion across the magnetic hard disk 106.
FIG. 2 provides an illustration of a head gimbal assembly (HGA) 204 and slider 202 as used in the art. Typically, a slider 202 (containing a read/write magnetic head; not shown) is utilized for maintaining a prescribed flying height above the disk surface 106 (See FIG. 1). During flight over the disk, electrostatic charge accumulates on a head's surface. If the charge is not removed, an electrostatic discharge (ESD) may occur, damaging the magnetoresistive (MR) element. Electrically-conductive adhesives are used in the art to bond head to suspension, allowing static charge to be discharged from the head 202 to the suspension (HGA) 204.
As the size of slider/head elements reduces to provide for increasing areal density, the energy necessary to cause damage by an ESD reduces, causing the likelihood for ESD to increase and rendering current methods of ESD prevention obsolete. For example, electrostatic current traveling from head to suspension through electrically-conductive adhesive may experience a resistance of greater than 1000 ohms at a one-volt potential, which is too large to meet giant magnetoresistive (GMR) heads' requirements for ESD prevention.
FIG. 3a-b illustrates a system for securing a head 302 to a suspension 304 (HGA) with an electrically conductive isotropic adhesive 307 as is used in the art. As seen in FIG. 3a, conductive isotropic adhesives 307, such as silver paste, contain conductive particles 311 (e.g., silver), which provide a pathway for electrostatic discharge from the head 302 to ground (suspension 304/HGA).
As shown in FIG. 3b, electrostatic (electrical) resistance is large for current passing through a typical isotropic adhesive 316 from head 312 to suspension 314 due to the distribution of conductive particles 320,322 within the head 312 and the isotropic adhesive 316. The head/slider 312 is typically made of Al2O3 319 and TiC 320 (together known as ALTIC). TiC 320 is electrically conductive, but Al2O3 319 is not. Silver epoxy, a typical isotropic conductive adhesive 316, is made of a binder resin 321 and silver powder 322. Silver powder 322 is electrically conductive, but binder resin is not. The internal distribution of these electrically conductive subparticles 320,322 causes the resistance problem. Although many TiC 320 particles may line up to provide an electrically conductive path toward the suspension 304, each TiC particle 320 terminating at the head 302/adhesive 306 interface has a low probability of being in physical contact with a particle of silver powder in the adhesive 306. Further, between each particle of silver 322 there is a this film of binder resin 321, which inhibits electrical current flow. Because of the small size of the silver particles 322, it can take several particles 322 to form an electrostatic discharge path, and thus, for each path there are several points in which the current must cross (highly resistive) binder resin 321, increasing the overall resistance across the isotropic adhesive.
It is therefore desirable to decrease head-to-suspension adhesive resistance to prevent electrostatic discharge (ESD) by the magnetic head as well as providing additional benefits.